Fibrous lubricating grease



Patented July 21, 1953 FIBnoUs LUBRICATING eREAs'E Rosemary -'Halloran,-' Elizabeth, N. J assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application April 28, 1950,

' Serial No. 158,933

6'Claims. (01. 252-40) This invention relates to improved lubricating compositions. More particularly, the invention relates to water resistant lubricating greases having improved fibrous structure.

It is known in the art that lubricating compositions having excellent water resistant properties can be prepared from lubricating oils thickened to a grease consistency with the calcium or lithium soapsof substantially saturated fatty acids or mixtures of the calcium and lithium soaps of these acids. These water resistant greases furnish satisfactory lubricating properties for a great number of industrial applications. However, due to the exceptionally smooth, unctuous and non-fibrous structure of these calcium and/or lithium soap base greases, they are not completely satisfactory for some industrial applications where the .lubricating parts are exposed. For example, in the lubrication of many different moving parts in the trucks, tractors, tractor rolls, mixers, cranes, etc. used in excavating, dumping, and carrying heavy loads for the construction and mining industries, a grease must be resistant to water and mud and must also be capable of forming aseal to prevent the entrance of dirt and etc. into the moving parts. The known water resistant greases, such as the calcium and/or lithium soap greases, due to their non-fibrous structure, tend to collect in one place and fall off and do not form the necessary heavy ring of sealing lubricant.

Prior attempts to solve this lubricating problem by admixing with the calcium and/or lithium base greases, additive agents such as high molecular weight polybu'tene and other tackiness agents have not always been completely successful since the stringiness effect of these additives is sometimes lost in dispensing these greases through shackles and other types of fittings.

of this invention, that grease compositions hav- 7 ing the desired resistance to water and desirable fibrous structure may be made by a special procto their transition temperatures. After the transition temperature has been reached the greases are further cooled by either panning or continuous grease cooling methods.

The transition temperature described here is a sharp break in the characteristics of the hot grease, during cooling in which it changes from a clear, viscous, homogeneous fluid to an opaque,

granular, semi-solid material. The soap solution (grease) just prior to this transition may be considered as supersaturated, possibly consisting of unstable agglomerates of liquid crystals, which rapidly change over to a definite crystalline structure once seedingoccurs. .Mllling of this solution results in a realignment of the structure of the precrystalline agglomerates, and when agitation is discontinued before actual crystallizatio-n takes place, this milling results in a desirable change in the structure of the resultant grease in the direction of making the structure more fibrous.

The greases of this invention are prepared by incorporating from-5 to 50% of a metal soap of unsaturated. acids in lubricating oil. vThe fatty acids preferably of iodine value or above and a quarter of the mineral oil is heated to about F. The metallic hydroxide, usually in the form of a water slurry, (boiling-Water solution the temperature raised slightly above the melting point of the soap. The temperature is held there until the batch is a homogeneous fluid with no curds of undispersed soap.

The above procedure represents well known methods of grease manufacture.

cooled to handling temperatures without agitation, it being general practice particularly to avoid all stirring in making lithium soap greases.

It has now been found, however, that if the lithium or lithium and calcium or lithium and strontium soap greases prepared in accordance with: the procedure described above are cooled from their melting points (usually about 380-400" F. in the case of lithium grease or 320-330 F. for

lithium -calcium grease) to their transition temperatures (about 340 F. for lithium and about According .to I the prior art, greases prepared in this manner are 3 280300 F. for lithium-calcium grease) with constant agitation, preferably a severe milling action and then cooled to handling temperatures (that is to a temperature at which the greases may be safely processed without danger) in a normal manner without agitation, there results a considerable increase in fibrous structure. The probable mechanism of this agitation step is that, as the soap begins to crystallize out immediately below its melting point, it is readily drawn into fibers by the stirring or milling operation. It .is important that the agitation cease immediately upon reaching the transition temperature for if the grease is agitated at temperatures-below the transition temperature the soap, becoming rapidly insoluble, forms into hard granules rather than into fibers. removed by an added cold milling step, but the desired fibrous, gutty, structure is lost due to the formation of the soap into hard granules.

The following examples list more specifically the present inventive concept.

EXAMPLE 1 A grease of the following formulation:

15.00% cottonseed fatty acids 1.90% lithium hydroxide monohydrate 0.85% lime (63% as CaO) 8225% coastal distillate, 900 S. U. S./ 100 F.

was prepared in the following manner.

The fatty acids and a quarter of the mineral oil were heated to 120 F. and the lime added. After this was completely cooked in, and the batch temperature about 170 F., a boiling water slurry or solution of lithium hydroxide was added and the temperature raised to 220 F. At this point another quarter of the oil charge was added to allow the soap concentrate to be stirred more easily and the batch held at 220 F.-240 F. until dehydration was completed. Then heating was resumed, the remainder of the mineral oil added at about 300 F., and the temperature brought up to 320 F. The temperature was held at that point until the batch was a homogeneous fluid with no curds of soap floating on top.

Samples of this batch were treated in various ways. Sample No. 1 was removed and heated to 360 F, and then pan cooled. Sample No. 2 was withdrawn from the grease kettle and panned at 320 F. The heat was removed from the grease kettle and stirring continued while the batch cooled. Samples No. 3 to No. 7 were removed at various temperatures as shown in the table below.

The cooled samples were worked 300 strokes in the fine hole worker plate grease worker to homogenize them and their fibrous structure measured. A test machine was designed especially for the measurement of fiber length and is described as follows:

Two vertical parallel steel rods, fastened to a fixed base support a pulley mechanism and furnish a guideway for a travelling circular contactingsurface. Attached to top of the moving circular contacting surface is a flexible cable to which is attached a weight. The cable is so ar- These soap particles may be I 7 ranged that when the weight moves downward the moving circular contacting surface guided by the parallel rods makes uniform contact with it. When the weight is raised the moving circular contacting surface is lowered until the two circular contacting surfaces touch. When the weight is released the two circular contacting surfaces separate. A calibration device is aifixed to the vertical rods so that thelength of a grease fiber suspended from the movable contacting surface may be measured.

In the operation of this tester a 2 gram sample of the grease is distributed evenl on the movable contacting surface and the weight is raised, lowering the movable contacting surface, until the surface is of an inch from the base, contacting the grease with the base surface. The weight is then released, the movable contacting surface pulled up with an initial quick movement which is damped by the hydraulic medium into which the weight descends, and 'is finally stopped gently by rubber bumpers at the top of the rods. The fiber length of the grease is determined as the average of 5-10 runs on the length of the grease string hanging from the movable contacting surface.

The grease samples prepared as above. were tested in this machine, the data being reported in Table I below.

TABLE I Effect of manufacture method on fiber length of lithium-calcium grease Strin Sample No. Temp. Appearance Drawn Inches 360 1.6 Smooth. 320 2.1 Do. 300 4.5 Do. 290 3.9 Do. 280 3.1 Slightly grainy. 240 2.5 Grainy. 150 2.8 Do.

These data indicate that stirring the grease between its melting point (328 F.) and its transition temperature (280 F.) results in a considerable increase in fibrous structure, l to 4 inches string length being obtained by this method as compared with an average of 2.4 inches for all the other methods. p

In the preparation of greases to develop the concept of this invention, that is, the improvement of fibrous structure by agitation or shearing of the grease in the p-recrystalline state, it is necessary to use unsaturated fatty acids in the grease formulations. It is desirable that the fatty acids be highly unsaturated, having an iodine value of approximately 100. The table below shows the properties of several greases prepared by the method of this invention using fatty acids of different degrees of unsaturation.

Lithium-calcium greases Hydr. ggg g Fish Cotton- Fatty Acid I Fish Acids-F seed Soyabean Acids Elghfle seed Iodine No 3 45 Top Temp., F 380 370 330 350 Pan Temp. F 350 340 290 275 Dropping Pomt, F 346 340 328 337 String Length, 11L l 1% 4 3% It will be observed also from these data that the transition temperature (panning temperature) drops with increasing iodine value of the fatty acids employed, thus allowing the grease to be stirred to a lower temperature.

EXAMPLE II A lithium base grease having the following formulation:

15.00% cotton seed fatty acids 3.00% lithium hydroxide monohydrate 82.00% coastal distillate, 900 S. U. S./l F.,

Effect of manufacture method on fiber length of lithium grease F. Temp- String Sample N o. erature Appearance Drawn Inches 1 400 2. 2 Smooth. 2 340 3. 5 Do.

Here again the fiber nature of the grease is increased by stirring down. 1

EXAMPLE III Although in the above two examples the agitation was carried out by a mixing procedure, it is also possible to mill the hot grease in a roll mill or other shearing or homogenizing machine. A lithium-calcium base grease prepared by the formulation and procedure of Example I above was heated to 320 F. One sample was transferred to a roll mill operating at 250 F., sheared for 2-3 minutes and then pan cooled. A second sample was milled at 290 F., the transition temperature of the grease, and then pan cooled. The sample milled at 290 F. had a very fibrous structure while that milled at 250 F. did not, as measured by the fiber length machine. These data are reported in Table III below.

TABLE III Effect of hot milling on the fiber structure of To summarize briefly, this invention comprises improved fibrous lubricating compositions and their manufacture. Lithium orlithium and calcium or stronthium soap greases are improved in their fibrous structure by agitation while cooling from the meltin point of the soap to the transition temperature.

Any of the commonly known additive materials may be added to the greases of this invention, to improve their properties in regard to oxidation, wear, rust protection, etc.

What is claimed is:

1. A process for the manufacture of an improved lubricating composition which comprises admixing with a lubricating oil the desired amount of a soap of a non-conjungated unsaturated fatty acid having an iodine number above about selected from the class consisting of lithium soaps, mixtures of lithium and strontium soaps, and mixtures of lithium and calcium soaps of unsaturated fatty acids, heating the mixture to the melting point of the soap, cooling the heat-' ed soap mixture to its transition temperature with agitation, and cooling the agitated grease mixture without agitation to a safe handling temperature.

2. In a process for the manufacture of improved grease compositions consisting of a lubricating oil thickened to a grease consistency with a soap selected from the class of lithium, lithium and strontium, and lithium and calcium soaps of non-conjugated unsaturated fatty acids having an iodine number above about 75, the improvement which comprises cooling the grease composition from the melting point of the soap to its transition temperature with constant agitation, and thereafer cooling the agitated grease composition to its handling temperature without agitation.

3. An improved process according to claim 2 wherein the grease composition is a lubricating oil thickened to a grease consistency with the lithium and calcium soaps of unsaturated fatty acids. 4. An improved process according to claim 2 wherein the grease composition is a lubricating oil thickened to a grease consistency with the lithium and strontium soaps of unsaturated fatty acids.

5. An improved process according to claim 2 wherein the grease composition is a lubricating oil thickened to a grease consistency with lithium soap of unsaturated fatty acids.

6. An improved lubricating composition which comprises a mineral oil thickened to a grease consistency with a soap selected from the class consisting of lithium, lithium and strontium, and lithium and calcium coaps of non-conjugated unsaturated fatty acids having iodine'numbers above about 75, the grease composition having been prepared by heating to the melting point of the soap, cooling to its transition temperature with constant agitation, and cooling to handling temperature without agitation.

ROSEMARY OHALLORAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,265,791 Zimmer et a1 Dec. 9, 1941 2,397,956 Fraser Apr. 9, 1946 2,495,651 Butcosk Jan. 24, 1950 2,503,969 Rude] et a1. Apr. 11, 1950 2,514,286 Morway July 4, 1950 OTHER REFERENCES Klemgardz Lubricating Greases, pg. 64-1937. I 

1. A PROCESS FOR THE MANUFACTURE OF AN IMPROVED LUBRICATING COMPOSITION WHICH COMPRISES ADMIXING WITH A LUBRICATING OIL THE DESIRED AMOUNT OF A SOAP OF A NON-CONJUNGATED UNSATURATED FATTY ACID HAVING AN IODINE NUMBER ABOVE ABOUT 75 SELECTED FROM THE CLASS CONSISTING OF LITHIUM SOAPS, MIXTURES OF LITHIUM AND STRONTIUM SOAPS, AND MIXTURES OF LITHIUM AND CALCIUM SOAPS OF UNSATURATED FATTY ACIDS, HEATING THE MIXTURE TO THE MELTING POINT OF THE SOAP, COOLING THE HEATED SOAP MIXTURE TO ITS TRANSITION TEMPERATURE WITH AGITATION, AND COOLING THE AGITATED GREASE MIXTURE WITHOUT AGITATION TO A SAFE HANDLING TEMPERATURE. 